An Uninterruptible Power Supply (UPS) is a constant-frequency, stable-voltage, pure, uninterruptible and high quality power supply. With the rapid development of information technologies and the wide applications of computers, the UPS has become an indispensable power supply device in numerous critical scenarios. Plural UPS units are often required to be parallelized to operate for improved reliability or an increased capacity. Parallelization signals are intended to enable the respective UPS units in a parallelized system to be aware of operating statuses of the others and to provide a reference for their own operations in view of these statuses. In order to ensure rapid and reliable parallelization, timely and reliable transmission of a large amount of information between the respective UPS units shall be ensured, and also a relatively long transmission distance shall be required. Therefore, the present parallelization communication generally transmits the parallelization signals in parallel. Although this transmission method has the advantages of being simple and rapid, it may be limited in terms of important aspects such as the transmission distance, tolerance, wiring, etc.
Signals were generally transmitted in parallel in prior parallelization communication methods. As illustrated in FIG. 1, a number, n, (n>1) of parallelization signals shall be transmitted for two parallelized UPS units, where an logic AND (i.e., “line-AND”) operation, is performed by a diode or a similarly functioning circuit on each signal while being transmitted, so that each UPS unit can acquire status information of the others. In FIG. 1, Sig_1_Tx and Sig_n_Tx represent a parallelization signal 1 and a parallelization signal n, which are transmitted from a UPS unit, and Sig_1_Rx and Sig_n_Rx represent a parallelization signal 1 and a parallelization signal n, which are received by the UPS unit. The use of the method illustrated in FIG. 1 for parallelization communication enables rapid interaction of the signals between the respective UPS units, but the number of required signal lines will increase as the number of parallelization signals increases. A large number of parallelization signal lines may cause complication and hence inconvenience of wiring. And, hardware circuits have to be redesigned once the number of parallelization signals increases, which may result in inflexibility. Moreover, the parallelization transmission process may be susceptible to interference and fail to satisfy the required long-distant transmission. More importantly, once one signal line is shorted with another or with a supply/ground, the system can not identify the short circuit due to the limitation of circuits.